1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a return path section.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate.
The write head unit in a magnetic head for perpendicular magnetic recording includes a coil, a main pole, and a return path section. The main pole and the return path section each have an end face located in a medium facing surface facing a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole produces a write magnetic field from its end face. The return path section is connected to the main pole so that a space through which part of the coil passes is defined by the main pole and the return path section. The return path section allows a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. The main pole and the return path section form a magnetic path for passing a magnetic flux corresponding to the magnetic field produced by the coil. A magnetic head for perpendicular magnetic recording having such a configuration is disclosed in, for example, U.S. Pat. No. 6,954,340 B2.
As the frequency of write signals is increased in order to provide higher recording density, it is required of the magnetic head to provide an improved rate of change in the direction of the magnetic flux produced from the end face of the main pole. To meet this requirement, it is desirable to reduce the length of the magnetic path formed by the main pole and the return path section.
Further, as the frequency of write signals is increased, the skin effect of magnetic flux becomes noticeable in the magnetic path formed by the main pole and the return path section. The skin effect of magnetic flux is the phenomenon that the magnetic flux density increases in the vicinity of the surface of a magnetic substance, whereas the magnetic flux density decreases inside the magnetic substance other than the vicinity of the surface thereof. The skin effect of magnetic flux raises the problem that as the frequency of write signals is increased, the magnetic path formed by the main pole and the return path section becomes unable to pass a large amount of magnetic flux therethrough.
In general, the return path section includes a portion that passes through inside the innermost circumference of the coil. This portion is particularly high in magnetic flux density. Hereinafter, this portion will be referred to as the flux concentrating portion. When the skin effect of magnetic flux becomes noticeable in the flux concentrating portion, the problem mentioned above becomes noticeable.
To address this problem, it is conceivable to increase the cross-sectional area of the flux concentrating portion. However, an increase in the cross-sectional area of the flux concentrating portion leads to an increase in the size of the coil and an increase in the total length thereof. This causes an increase in the length of the magnetic path formed by the main pole and the return path section and an increase in the resistance of the coil.
Thus, it has conventionally been difficult to inhibit a decrease of magnetic flux caused by the skin effect of magnetic flux while preventing an increase in the length of the magnetic path formed by the main pole and the return path section and an increase in the resistance of the coil.